<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>

    .beijing{
        height: 500px; width: 500px; border: 10px solid ;
        background-image: linear-gradient(to bottom, aqua ,green);
    }

</style>
<body>
    <div class="beijing">

    </div>
</body>
</html>